Mobile stations, often denoted user equipment, have a need to measure various network parameters. Such measurements may be stored in measurement logs and then reported to the network.
The Third Generation Partnership Project (3GPP) is in the process of defining solutions for Minimizing Drive Tests (MDT). The intention of the work is documented in 3GPP Technical Report (TR) 36.805, where mobile stations or user equipment (UE) measurement logging functions are described.
A network (NW) can request the mobile station to perform some logging of measurements. The mobile station executes the logging as requested by the network with certain constraints, e.g. location information availability. Reporting of mobile station measurement log can be separately configured. This means that the period of logging and that for reporting can be different.
The most important use case for MDT is coverage optimization. For coverage optimization, the following mobile station measurements (or similar functionality) are considered:                periodic downlink pilot measurements        Serving Cell becomes worse than threshold        transmit power headroom becomes less than threshold        Paging Channel failure, such as Paging Control Channel (PCCH) Decode Error        Broadcast Channel failure        
The details of the reporting criteria have not been considered, but real-time reporting and/or non-real-time reporting (also known as logged or deferred reporting) can be required.
Possible triggers for non-real-time measurements include:                periodical downlink pilot measurements: radio environment measurements, such as Common Pilot Channel (CPICH) Received Signal Code Power (RSCP), Common Pilot Channel Energy per chip to Noise ratio (CPICH Ec/No), or Time Division Duplexing (TDD) Primary Common Control Physical Channel (P-CCPCH) Received Signal Code Power (RSCP) and Interference Signal Code Power (ISCP), Reference Signal Received Power (RSRP) and Reference Signal Received Quality (RSRQ) (connected mode only) are logged periodically;        Serving Cell becomes worse than threshold: radio environment measurements, such as CPICH RSCP, CPICH Ec/No, or TDD P-CCPCH RSCP and ISCP, RSRP and RSRQ (connected mode only), are logged when the serving cell metric becomes worse than the configured threshold. A measurement logging window (i.e. “sliding window” in which collected logs are kept in the UE) is used in order to be able to collect information during a certain period before and after the occurrence of event;        transmit power headroom becomes less than threshold: transmit power headroom and radio environment measurements, such as CPICH RSCP, CPICH Ec/No, or TDD P-CCPCH RSCP and ISCP, RSRP and RSRQ (connected mode only) are logged when UE transmit power headroom becomes less than the configured threshold;        random access failure: details on the random access and radio environment measurements, such as CPICH RSCP, CPICH Ec/No, or TDD P-CCPCH RSCP and ISCP, RSRP, and RSRQ (connected mode only) are logged when a random access failure occurs.        
An example of real-time reporting is radio resource management (RRM) reporting specified in 3GPP Technical Specification (TS) 25.331 and 3GPP TS 36.331. The details of non-real-time reporting (deferred reporting) are not specified, making it impossible for the network to control the reporting.
One particular issue is the support of the non-real-time reporting in the network. Not all network nodes may be upgraded to support reception of the non-real-time reports, potentially leading to the network discarding the received logged measurement report. Currently the mobile station has no way to know if the network is prepared to receive the logged measurement report.